1. Field of the Invention
Example embodiments of the general inventive concept relate to phase shift masks and method of forming phase shift masks. More particularly, example embodiments of the present general inventive concept relate to phase shift masks to prevent a haze defect as a result of a cleaning with alkaline chemicals, and method of forming the phase shift masks.
2. Description of the Related Art
As semiconductor devices have been developed to improve integration, reliability, and response speed, the dimensions of various elements in an integrated circuit device have been reduced. Recently, the elements in semiconductor devices have been manufactured with very minute critical dimension (CD) below about 0.07 μm. The reduction of the dimensions of the semiconductor devices may require that various minute patterns included in the semiconductor device have a higher resolution.
To obtain a minute pattern having high resolution, various resolution enhancement technologies (RET) have been employed in semiconductor manufacturing processes. For example, to ensure irradiating of a light onto a minute region of an object, the number of the numerical aperture may be increased, a dipole illumination procedure or a cross-pole illumination procedure may be employed, or a light having a short wavelength may be used as a light source in an exposure process. The light for forming a minute pattern may include a krypton fluoride (KrF) eximer laser having a wavelength of about 248 nm, an argon fluoride (ArF) eximer laser having a wavelength of about 193 nm, or a fluorine (F2) eximer laser having a wavelength of about 157 nm, for example.
When a minute pattern is formed using the light having the short wavelength, a depth of focusing (DOF) of the exposure process may be deteriorated although the minute pattern may have improved resolution. Thus, a phase shift mask (PSM) has been developed to form a minute pattern having desired resolution instead of the use of the light having the short wavelength.
A conventional phase shift mask usually includes a phase shift layer formed by forming recesses in a predetermined portion of a transparent substrate having a metal layer coated thereon. The phase shift layer may transmit light through different light passages thereof, and thus the light transmitted through one passage may have a phase difference of about 180° from light passing through adjacent openings of the phase shift mask. The light having the phase difference of about 180° may cause destructive interference, so that the intensity of the lights may be diminished or reduced substantially to zero.
Generally, a cleaning process is performed on the phase shift mask to completely remove contaminants remaining on a surface of the phase shift mask before forming a minute pattern having high resolution using the phase shift mask. As for a cleaning process to clean the conventional phase shift mask including a single chrome (Cr) layer or having a structure including a chrome layer and a molybdenum silicon (MoSix) layer, the contaminants (e.g., a photoresist pattern used for forming the phase shift mask, polymers generated in an etching process, etc.) may be completely removed from the phase shift mask. The conventional phase shift mask is generally cleaned using a cleaning solution including sulfuric acid (H2SO4). After cleaning the phase shift mask, a rinsing process is executed on the cleaned phase shift mask using deionized (DI) water having high temperature. However, the rinsing process may not completely remove the cleaning solution including sulfuric acid from the phase shift mask because the cleaning solution has relatively high viscosity. Therefore, haze defects may be generated on the phase shift mask due to the cleaning solution remaining on the phase shift mask.
Meanwhile, the phase shift layer of the phase shift mask may be damaged by hydroxyl group (—OH) in ammonium hydroxide (NH4OH) when the phase shift mask is cleaned using a standard cleaning 1 (SC1) solution. The damaged phase shift layer may cause defects of the phase shift mask. As a result, a minute pattern having desired high resolution may not be obtained using such phase shift mask because of phase shift of light and transmittance variation of light.
Considering the above-described problems, the phase shift mask is rinsed using a solution including diluted ammonium hydroxide reacting with sulfuric acid. However, the sulfuric acid may not be fully removed from the phase shift mask because relatively weak ammonium hydroxide may not effectively neutralize sulfuric acid causing the haze defects of the phase shift mask. Therefore, the phase shift mask may not produce the minute pattern having the desired high resolution because of the remaining contaminants that cause the haze defects of the phase shift mask.